CALAIS, France—At least 31 migrants bound for Britain died Wednesday when their boat sank in the English Channel. French Interior Minister Gerald Darmanin said 34 people were believed to have been on the boat. Authorities found 31 bodies—including those of five women and a young girl—and two survivors, he said. One person appeared to still be missing. The nationalities of the travelers was not immediately known. A joint French-British search operation for survivors was called off late Wednesday. Both countries cooperate to stem migration across the Channel. Four suspected traffickers were arrested Wednesday on suspicion of being linked to the sunken boat, Darmanin told reporters in the French port city of Calais. He said two of the suspects later appeared in court. The regional prosecutor opened an investigation into aggravated manslaughter, organized illegal migration and other charges after the sinking. Lille Prosecutor Carole Etienne, whose office is overseeing the investigation, …